Field of the Invention
The present invention relates to an etching method and an etching apparatus of a tungsten film.
Background Art
High integration of a semiconductor device, which is drawn by spread of a mobile device which is represented by a smartphone, is developed. In the field of a recording semiconductor, a three-dimensional (3D) NAND flash memory which is obtained by multilayeredly stacking memory cells in a three-dimensional direction is mass-produced, and the number of stacking memory layers is currently 64 layers. In the field of a logic semiconductor, a fin-type field effect transistor (FET) having a three-dimensional structure becomes a mainstream. A gate length of the FET is steadily shortened, and advent of an era of the gate length which is less than a 10 nm generation is expected.
In this manner, three-dimensional making of an element structure, and reduction of a processing dimension progress, accordingly, a need for an etching technology having both isotropy and high processing dimension controllability in an atomic layer level is increased, in a device manufacturing process.
In the related art, as an isotropic etching technology, a wet etching technology such as etching of a silicon dioxide using a mixed aqueous solution of hydrofluoric acid and ammonium fluoride, etching of a silicon nitride using heat phosphoric acid, or etching of tungsten using a liquid mixture of hydrofluoric acid and nitric acid has been widely used. However, in the wet etching technology of the related art using a wet chemical solution, there is a problem that pattern collapse due to surface tension of a rinse liquid becomes apparent, in accordance with the shrinkage of a pattern.
For example, in a case where a high aspect ratio pattern of silicon is used, when a pattern interval is narrowed, it is reported that a limit value of the pattern interval in which the collapse begins due to the surface tension at the time of drying the rinse liquid becomes large in proportion to a square of the aspect ratio. Therefore, it is strongly desired to develop a process method of isotropically etching various films without using the wet chemical solution.
Tungsten is a material that is widely used in a semiconductor device manufacturing process, as a material for an electrode or wiring. Therefore, in the next generation semiconductor device manufacturing process, there is a need for the tungsten etching technology having all of isotropy, high processing dimension controllability in the atomic layer level, and high selectivity.
In the related art, as an isotropic tungsten etching technology in which the wet chemical solution is not used, a method of isotropically etching tungsten at an etching speed exceeding 160 nm/minute by supplying a fluorine radical using plasma of NF3/O2, is published in Journal of Electrochemical Society, vol. 142, No. 6, 1971 (1995) written by Patrick Verdonck, Jacobus Swart, Guy Brasseur, and Pascal De Geyter.